This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 2001-359135 filed in JAPAN on Nov. 26, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a multi-piece solid golf ball comprising a solid core covered with a polyurethane cover.
2. Description of the Related Art
An ionomer resin cover has been widely used as a cover for a solid golf ball in which a vulcanized rubber sphere is used as a solid core, because of its excellent durability. However, compared to the balata rubber cover, the ionomer resin cover tends to give a far inferior shot feeling to the golfer when hitting the golf ball.
To improve the shot feel of the ionomer resin cover, a cover comprising an ionomer mixture has been proposed in Japanese Patent No. 2,709,950, where a hard ionomer which is a sodium or zinc salt of an olefin-unsaturated carboxylic acid copolymer is mixed with a soft ionomer which is a sodium or zinc salt of an olefin-unsaturated carboxylic acid-unsaturated carboxylic ester terpolymer. The shot feeling can be softened by blending this soft ionomer, but on the other hand, the advantages inherent in the ionomer cover are sacrificed, such as abrasion resistance (scratch resistance) and resilience.
Recently, polyurethane has been focused on as an inexpensive cover material that imparts to the golfer a shot feeling like the balata cover and has greater durability than balata. For example, a polyurethane cover comprising a urethane prepolymer which has been hardened with a slow-reacting polyamine curing agent is disclosed in Japanese Patent No. 2,662,909.
There is a problem in forming the polyurethane cover. The problem is that it is difficult to form the cover because the rapid reaction between the urethane prepolymer and polyamine curing agent results in a precipitous increase in viscosity. Although the slow-reacting polyamine curing agent is used in Japanese Patent No. 2,662,909 to prevent the rapid increase in viscosity resulting from the progress of the reaction between the urethane prepolymer and polyamine curing agent, it is still sometimes difficult to mold the cover, because of the rapid increases in viscosity, depending on the type of urethane prepolymer, type of curing agent, combination thereof, and the like. Even if the cover can be formed, further improvement is also needed, because the resilience, spin performance, and abrasion resistance are not altogether satisfactory.
In view of the foregoing, an object of the present invention is to provide a solid golf ball having a polyurethane cover, which satisfies the formability and the golf ball properties.
The golf ball of the present invention comprises
a solid core composed of at least one layer, and
a polyurethane cover for covering the solid core, wherein
the polyurethane cover has a thickness of from 0.2 to 0.5 mm, and is formed from a cured urethane composition having Shore D hardness of from 30 to 55;
the urethane composition comprises an isocyanate group-terminated urethane prepolymer and an aromatic polyamine compound; and
the deformation amount of the golf ball is from 2.40 to 3.30 mm when applying a load of from 98N as an initial load to 1275N as a final load to the golf ball.